What defines a one-time password?

A one-time password (OTP) is specifically designed for security purposes to enhance authentication processes. Its defining characteristic is that it is only valid for a single login session or transaction. Once it has been utilized, it expires immediately and cannot be used again. This means that even if an unauthorized individual were to obtain it, they would not be able to reuse it for subsequent access attempts, greatly reducing the risk of unauthorized access.

In contrast, other options refer to concepts that do not align with the nature of a one-time password. Reusable passwords, for example, do not provide the same level of security, as they can be intercepted and reused by malicious actors. Similarly, a password stored for later use would contradict the ephemeral nature of an OTP, as its value is intended to be transient and non-reliable for future sessions. Finally, the implication that OTPs are required for all users at all times suggests a universal application that may not be practical or necessary, as different systems may employ various authentication methods based on their specific security requirements.